Typically known as the structure of a railcar is a structure in which a keystone plate is arranged on an underframe constituted by end beams, side sills, center sills, bolster beams, and cross beams. Since a high compressive load acts on a railcar end portion of the underframe, a structure in which the stiffness and strength of the underframe are increased has been proposed (see PTL 1, for example). In the underframe described in PTL 1, a longitudinal frame member made of a fiber-reinforced composite material is provided at the center sill arranged between the bolster beams. With this, the underframe described in PTL 1 has a structure advantageous to a high railcar end load.